Germanium: From Its Discovery to High Speed

Germanium: From
Its Discovery to High
Speed Transistors
E.E. Haller
UC Berkeley & LBNL
EECS Solid State Seminar
March 18, 2011
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E. E. Haller
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Topics to be discussed
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Discovery of Germanium and Early History
From the “Physics of Dirt” to a Respectable Science
Point Contact Diodes and Transistors
Applications of Germanium in Nuclear Physics: GeLi and
High-Purity Ge detectors
New Physics with Ultra-Pure Germanium
Infrared Photoconductors and Bolometers
Isotopically Controlled Germanium
Germanium Speeds Up Silicon Transistors
E. E. Haller
2
Anno 1886
•
Discovery of a new element in the IVth column: Germanium by
Clemens Winkler: C. Winkler, “Mittheilungen über das Germanium,”
J. für Prakt. Chemie 34(1), 177-229 (1886)
•
The first 4-wheel motor car by Daimler & Benz
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Coca-Cola is formulated in Atlanta by a pharmacist
•
Walter Schottky is born, the future father of the metal-semiconductor
theory
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Elemental Fluorine is isolated by Moisson
•
Patents are filed in the US and Great Britain for the mass production of
Aluminium
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D.I. Mendelejev and C.A. Winkler at the meeting of the 100th anniversary of
the Prussian Academy of Science, Berlin, March 19, 1900.
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Topics to be discussed
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3/18/2011
Discovery of Germanium and Early History
From the “Physics of Dirt” to a Respectable Science
Point Contact Diodes and Transistors
Applications of Germanium in Nuclear Physics: GeLi and
High-Purity Ge detectors
New Physics with Ultra-Pure Germanium
Infrared Photoconductors and Bolometers
Isotopically Controlled Germanium
Germanium Speeds Up Silicon Transistors
E. E. Haller
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From the “Physics of Dirt” to a
Respectable Science
Karl Lark-Horovitz joined the
Physics Dept., Purdue
University in 1929. In 1942 he
made the fateful decision to
work on Germanium,
Germanium not on
Galena (PbS) or Silicon. The
first transistor was built at Bell
labs with a slab of Purdue
Germanium! Based on the
Purdue work, Germanium
became the first controlled and
understood semiconductor.
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Purdue University Results
Karl Lark-Horovitz
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Purdue University Results
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Purdue University Researchers
Louise Roth
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Ge single crystal
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Anant K. Ramdas
(50th anniversary!)
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Topics to be discussed
•
•
•
•
•
•
•
•
3/18/2011
Discovery of Germanium and Early History
From the “Physics of Dirt” to a Respectable Science
Point Contact Diodes and Transistors
Applications of Germanium in Nuclear Physics: GeLi and
hpGe detectors
Physics with Ultra-Pure Germanium
Infrared Photoconductors and Bolometers
Isotopically Controlled Germanium
Germanium Speeds Up Silicon Transistors
E. E. Haller
10
Point Contact Diodes and Transistors
•
How to detect the weak radar pulse echoes?
•
Cat’s whisker metal point contacts to polycrystalline Ge
and Si formed diodes sufficiently fast to work as mixers
for radar reception in WWII
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“Tapping” rectifiers to optimize their performance
E. E. Haller
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The MIT Radiation Laboratory
The title page of MIT’s
Radiation
Laboratory Series
Volume 15.
This series gives a
detailed
account of the Radar
R&D activities
at MIT during WWII.
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!
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Discovery of the Transistor
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Controlling big power with little effort: amplification
The Bell labs vision: Mervin J. Kelly
Minority carrier injection and lifetime
December 24, 1947
The point contact transistor: shows the principle of
amplification but is very fragile (J. Bardeen and W.
Brattain)
The junction transistor (W. Shockley)
Are single crystals required?
The generations of Ge and Si transistors: point contact Ge
transistor Ge junction transistor alloyed Ge transistor
Ge mesa transistor (fmax = 500 MHz, Charles Lee, 1954)
Si planar transistor (Jean A. Hoerni, 1960)
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The first transistor fabricated by Bell Laboratories’ scientists
was this crude point-contact device, built with two cat’s
whiskers and a slab of polycrystalline germanium.
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Point contact
transistor
schematic
The famous lab book entry of
Christmas eve 1947:
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William Shockley,
John Bardeen and
Walter Brattain (left
to right) are gathered
together around an
experiment in this
historic 1948 photograph. The first
point contact transistor remains on
display at AT&T
Bell Labs in
Murray Hill, New
Jersey.
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Is Polycrystalline Material Reproducible?
Variation in melting practice and its effect on the physical
characteristics of the silicon ingot
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Jan Czochralski
Sketch of
a modern
CZ-puller
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Teal and Little’s Hard Fought Victory*
Uniformity of crystal geometry obtainable with the pulling
technique (i.e., the Czochralski technique).
*G.K. Teal and J.B. Little, Phys. Rev., 78 (1950) 647
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The First Semiconductor
Energy Band Structure
Physical Review 89(2) 518-9 (1953)
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The First Integrated Circuit
The first integrated germanium circuit built by J. Kilby at
Texas Instruments in 1958.
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Topics to be discussed
•
•
•
•
•
•
•
•
3/18/2011
Discovery of Germanium and Early History
From the “Physics of Dirt” to a Respectable Science
Point Contact Diodes and Transistors
Applications of Germanium in Nuclear Physics: GeLi and
High-Purity Ge detectors
New Physics with Ultra-Pure Germanium
Infrared Photoconductors and Bolometers
Isotopically Controlled Germanium
Germanium Speeds Up Silicon Transistors
E. E. Haller
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Applications of Germanium in Nuclear
Physics: GeLi and hpGe Detectors
First Li drifted p-i-n Ge
diode: D. V. Freck and J.
Wakefield, Nature 193, 669
(1962)
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Ultra-Pure Ge: NA-ND 2x1010cm-3
The Lawrence
Berkeley Laboratory
ultra-pure germanium
growth apparatus. A
water-cooled RFpowered coil surrounds
the silica envelope of
the puller. About half
of the 25 cm long
crystal has been grown.
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The Berkeley High-Purity Ge Team
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Dopant Impurity Profiles
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Impurity profiles in an ultra-pure Ge crystal with some boron (B, dotdash line) segregating towards the
end contaminates the crystal.
E. E.seed
Haller
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Ultra-pure germanium detector with closed-end coaxial contact geometry. The borehole
reaches to within in ~ 2 cm of the backsurface of the p-i-n device and forms one contact.
The whole outside surface except the flat portion surrounding the hole forms the other
contact. Large volume detectors with small capacitance can be achieved with the coaxial
geometry. (Courtesy of P.N. Luke, Lawrence Berkeley National Laboratory)
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Topics to be discussed
•
•
•
•
•
•
•
•
3/18/2011
Discovery of Germanium and Early History
From the “Physics of Dirt” to a Respectable Science
Point Contact Diodes and Transistors
Applications of Germanium in Nuclear Physics: GeLi and
High-Purity Ge detectors
New Physics with Ultra-Pure Germanium
Infrared Photoconductors and Bolometers
Isotopically Controlled Germanium
Germanium Speeds Up Silicon Transistors
E. E. Haller
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Physics with Ultra-Pure Germanium:
Exciton Condensation
After C. D. Jeffries, Science 189(4207), 955 (1971)
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Electron-Hole Drops
Photograph of a long-lived
electron-hole drop in a 4mm disk of ultra-pure
germanium. The sample is
mounted in a dielectric
sample holder and stressed
by a 1.8-mm-diam screw
discernible on the left.
See: J. P. Wolfe, W. L.
Hansen, E. E. Haller, R. S.
Markiewicz, C. Kittel, and C.
D. Jeffries, Phys. Rev. Lett.,
34 (1975) 1292.
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Hydrogen Permeation Studies
with Crystalline Germanium
Ref.: R.C. Frank and J.E. Thomas Jr., J. Phys. Chem. Solids 16, 144 (1960)
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Self-Counting Tritium Doped
Ultra-Pure Ge Detector
Tritium Labeling*:
3
3
T
2 He
1
Samples taken from tritiumatmosphere-grown ultra-pure
Ge crystal at different
locations were fashioned into
radiation detectors, counting
the internal T decays. The H
concentration varies between
5x1014 and 2x1015 cm-3.
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[*Ref.: W.L . Hansen, E.E.
Haller and P.N. Luke, IEEE
Trans. Nucl. Sci. NS-29, No.
1, 738 (1982)]
33
Hydrogen and Dislocations in Ge
(Preferentially etched (100) Ge surface)
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Ref.: E. E. Haller et al., Inst. Phys. Conf. Ser. 31, 309 (1977)
E. E. Haller
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Hydrogen and Dislocations in Ge
(Preferentially etched (100) Ge surface)
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Ref.: E. E. Haller et al., Inst. Phys. Conf. Ser. 31, 309 (1977)
E. E. Haller
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The V2H Center in Dislocation Free,
H2 Atmosphere Grown Germanium
(V2H)
V2H (EV+80meV)+ H
V2H2 (neutral)
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Log (hole concentration) against
reciprocal temperature 1/T of a
dislocated (+) and an undislocated
(o) Ge sample cut from the same
crystal slice. The net impurity
concentration of shallow
acceptors and donors is equal for
both samples. The V2H acceptor
(Ev + 80 meV) only appears in the
dislocation free piece (rich in
vacancies); its concentration
depends on the annealing
temperature, [Ref.: E. E.Haller et
al., Proc. Intl. Conf. on Radiation
Effects in Semiconductors 1976,
N.B. Urli and J.W. Corbett, eds.,
Inst. Phys. Conf. Ser. 31, 309
(1977)]
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Photo Thermal Ionization
Spectroscopy (PTIS)
(from the thermal bath)
(from the spectrometer)
PTIS: Photo-Thermal Ionization Spectroscopy allows the study of extremely low
dopant concentration [as low as 1 acceptor (donor) in 1014 host atoms]
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Typical PTI Spectrum of
ultra-pure germanium.
The 555 mm3 piece of
the crystal had two ion
implanted contacts on
opposite faces. The netacceptor concentration is
21010 cm-3. Because of
the high resolution, the
small lines of B and Ga
can be seen clearly.
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Discovery of an Isotope Shift in the Ground State
of the Oxygen-Hydrogen Donor and the SiliconHydrogen Acceptor in Germanium
pure H2
51 eV
isotope
shift!
pure D2
3/18/2011
Ref.: E.E. Haller, Phys. Rev. Lett. 40, 584 (1978)
E. E. Haller
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Topics to be discussed
•
•
•
•
•
•
•
•
3/18/2011
Discovery of Germanium and Early History
From the “Physics of Dirt” to a Respectable Science
Point Contact Diodes and Transistors
Applications of Germanium in Nuclear Physics: GeLi and
High-Purity Ge detectors
New Physics with Ultra-Pure Germanium
Infrared Photoconductors and Bolometers
Isotopically Controlled Germanium
Germanium Speeds Up Silicon Transistors
E. E. Haller
40
Extrinsic Ge Photoconductors for Far
Infrared Astronomy
Interest: the far IR spectral range (50 to 2000 m) contains
information of great interest for the chemical composition of
the Universe (vibrational and rotational molecular bands), for
galaxy, star and planet formation and evolution, for views
through cold and warm dust
Far IR
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Extrinsic Ge Photoconductors
•
•
Shallow dopants in Germanium have ionization energies near
10 meV (corresponding to 80 cm-1 or 125 m). The low
temperature photoconductive onset at max 125 m lies in
the far IR.
Three generations of photoconductors:
Far IR
photons
Far IR
photons
Ge:Ga photoconductor
(5x5x5mm3,
max 125m )
before 2000
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Blocking Layer
Far IR
photons
Absorbing
Layer
Stressed Ge:Ga
photoconductor
(5x5x5mm3,
max 230m )
current
E. E. Haller
Ge:Ga
Blocked Impurity
Band detector
(max > 250m )
after 2007
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The Spitzer Space Telescope
- Launched in August
2003 on a two stage
Delta rocket with 9 solid
fuel boosters
- The liquid He cooled
0.85 m telescope is
on an earth orbit
vis-à-vis the earth
- wavelength range 3m
< l < 180m
- Lifetime : up to 5 years
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Observations with Ge Photoconductors
From visible
light to the
far infrared.
Galaxy
Messier 81
at a distance
of 12 Million
light years!
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Neutron Transmutation
Doped (NTD) Germanium
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Irradiation of Ge with thermal neutrons
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Homogeneous impurity distribution reflects uniform neutron flux and uniform
Neutron captures and decays:
EC
71
31
Ga (acceptor)
11.2d
74
75
75
33
As (donor)
32 Ge(n, ) 32 Ge
82.2m
76
77
3477 Se (double donor)
32 Ge(n, ) 32 Ge
11.3h
70
32
Ge(n, ) 3271Ge
isotopic distribution
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Reproducibility: NGa = 70 N70
Ge
Ge
Ultra-pure starting material
Neutron doping levels >> residual impurities
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R versus T-1/2 for several NTD Ge
Thermistors
= o exp (To/T)1/2
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Silicon Nitride Micromesh
‘Spider-web’ NTD Ge Bolometers
Spider-web architecture provides
low absorber heat capacity
minimal suspended mass
low-cosmic ray cross-section
low thermal conductivity = high sensitivity
Sensitivities and heat capacities achieved to date:
NEP = 1.5 x 10-17 W/Hz, C = 1pJ/K at 300 mK
NEP = 1.5 x 10-18 W/ Hz, C = 0.4 pJ/K at 100mK
Detectors baselined for ESA/NASA Planck/HFI
Arrays baselined for ESA/NASA FIRST/SPIRE
Planned or operating in numerous sub-orbital experiments:
BOOMERANG
SuZIE
MAXIMA
BOLOCAM
ACBAR
BICEP
Archeops
BLAST
Z-SPEC
QUEST
Caltech
Stanford
UC Berkeley
CIT/CU/Cardiff
UC Berkeley
Caltech
CNRS, France
U. Penn
Caltech
Stanford
Antarctic balloon CMB instrument
S-Z instrument for the CSO
North American balloon CMB instrument
Bolometer camera for the CSO
Antarctic S-Z survey instrument
CMB polarimeter
CMB balloon experiment
Submillimeter balloon experiment
Mm-wave spectrometer
CMB polarimeter
Courtesy J. Bock, NASA-JPL
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Metal-Insulator Transition with NTD 70Ge
= o exp (To/T)1/2
The left side shows the experimentally determined T0 of 14 insulating
samples as a function of Ga concentration (). The right side shows the
zero temperature conductivity (0) obtained from the extrapolations (T) for ten metallic samples as a function of Ga concentration (•).
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K. M. Itoh, et al., Phys. Rev. Lett. 77(19), 4058-61 (1996).
E. E. Haller
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Topics to be discussed
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•
•
•
•
•
•
•
3/18/2011
Discovery of Germanium and Early History
From the “Physics of Dirt” to a Respectable Science
Point Contact Diodes and Transistors
Applications of Germanium in Nuclear Physics: GeLi and
High-Purity Ge detectors
New Physics with Ultra-Pure Germanium
Infrared Photoconductors and Bolometers
Isotopically Controlled Germanium
Germanium Speeds Up Silicon Transistors
E. E. Haller
49
STABLE ISOTOPES
75As
70Ge, 72Ge, 73Ge, 74Ge, 76Ge
69Ga, 71Ga
Z
N
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95% ENRICHED, ULTRA-PURE Ge SINGLE CRYSTALS
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Excitons in 70Ge, nat.Ge and 74Ge
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Courtesy Gordon Davis, et al.
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Thermal Conductivity of Solids
Valery Ozhogin and
Alexander Inyushkin,
Kurchatov Institute,
Moscow
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Change of the direct Ge Bandgap with Isotope Mass
C. Parks, et al., Phys. Rev B. 49, 14244 (1994)
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Self-Diffusion in Isotope Structures
74Ge
(> 96%)
70Ge
(> 95%)
After annealing (55 hrs / 586˚C)
natGe
natG
e
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H. Fuchs et al., Phys. Rev. B 51,
16871 (1995)
55
The First Ge Isotope Superlattice
G. Abstreiter, Munich
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Raman Lines of the Ge Isotope Superlattice
Experiment
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Theory
E. E. Haller
Spitzer, et al., Phys.
Rev. Lett. 72, 1565
(1994)
57
Topics to be discussed
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•
•
•
•
•
•
•
3/18/2011
Discovery of Germanium and Early History
From the “Physics of Dirt” to a Respectable Science
Point Contact Diodes and Transistors
Applications of Germanium in Nuclear Physics: GeLi and
High-Purity Ge detectors
New Physics with Ultra-Pure Germanium
Infrared Photoconductors and Bolometers
Isotopically Controlled Germanium
Germanium Speeds Up Silicon Transistors
E. E. Haller
58
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Summary
• The 120 year history of the element Ge is rich in
science and technology
• Today Ge has returned to mainstream electronics
because of its excellent transport properties and
engineering of bandstructures using strain
• More interesting findings will be made…Long live
Germanium!
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EXTRAS
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Pure H2 atmosphere
Mixed atmosphere:
H/D = 1/1
Pure D2 atmosphere
The D(O,H) donor in Ge contains exactly one H atom!
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E.
E. Haller 5/18/2010
Ref.: E. E. Haller, Inst. Phys. Conf. Series 46, 205 (1979)
E. E. Haller
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The Acceptor A(H,C) in
Ultra-Pure Germanium
Ref.: E. E. Haller, B.Joos and L. M. Falicov,
Phys. Rev. B 21, 4729 (1980)
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•The groundstate of A(H,C) is split
by 1.98 meV, leading to two series
of ground-to-bound excited state line
series (blue and red). The intensity
ratio of corresponding lines is proportional to a Boltzmann factor
exp [1.98 meV/kBT ].
• Only crystals grown in a H2
atmosphere from a graphite crucible
contain this acceptor.
• Upon substitution of H with D the
ground state shifts by 51 eV to lower
energies.
• Joos et al., Phys. Rev. B 22, 832
(1980) modeled this center with
a tunneling hydrogen complex.
E. E. Haller
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The Acceptor A(H,Si) in Ultra-Pure
Germanium
• The groundstate of A(H,Si) is split
Ref.: E. E. Haller, B.Joos and L. M. Falicov,
Phys. Rev. B 21, 4729 (1980)
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by 1.07 meV, leading to two series
of ground-to-bound excited state line
series (blue and red). The intensity
ratio of corresponding lines is proportional to a Boltzmann factor
exp [1.1 meV/kBT ].
• Only crystals grown in a H2
atmosphere from a SiO2 crucible
contain this acceptor.
• Upon substitution of H with D the
ground state shifts by 21 eV to lower
energies.
• Kahn et al., Phys. Rev. B 36, 8001
(1987) modeled this and other centers
[A(H,C), A(Be,H), A(Zn,H)] with
trigonal complexes.
68
The Cu triple
acceptor in Ge binds
up to three
interstitial H or Li
atoms. Each bound
H or Li reduces the
number of
electronic states by
one (i.e., CuH3 is
neutral)
Position of the acceptor levels of copper and its complexes with hydrogen and lithium in
germanium. [Ref.: E.E. Haller, G.S. Hubbard and W.L. Hansen, IEEE Trans. Nucl. Sci.
NS-24, No. 1, 48 (1977)]
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Hillocks or dimples?
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Neutron Transmutation Doped Ge
Thermistors for Bolometers
Bolometers have two components: an absorber (TeO2) and
a thermometer (NTD Ge)
•Thermometer and absorber (heat
capacity C) are connected by a weak
thermal link (G) to a heat sink (To)
•Incoming energy is converted to heat
in the absorber:
T=To +(Psignal + Pbias)/C
•Temperature rise is proportional to the
incoming energy
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•Temperature rise decays as energy
flows from the absorber to heat sink:
= C/G
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CUORE/CUORICINO Double Beta
Decay:An Italian-US Experiment
• Absorber: TeO2 single crystals,
~ 1000 kg
• Temperature: 5 mK
• Thermal Sensors: NTD Ge
• Support: Copper, Teflon
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X-Ray Performance: Single
X-Ray Counting
0.35 mm x 0.35 mm x 7 m tin absorber + NTD 17 Ge thermistor
A publication describing an earlier measurement of 3.08 eV is: E. Silver, J. Beeman, F. Goulding, E.E. Haller, D. Landis and N. Madden,
Nuclear Instruments and Methods in Physics Research, Volume 545, 3, (2005), 683-689.
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Courtesy Eric Silver, Harvard
74
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H. Mataré 2003
H. Welker 1970
Working in Paris at the Westinghouse research laboratories, Herbert Mataré and
Heinrich Welker made transistor observations using multipoint contacts. Welker
went on to discover III-V compound semiconductors in the early 1950s, opening the
world of optoelectronics.
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After annealing (55 hrs / 586˚C)
natGe
H. Fuchs et al., Phys. Rev. B
51, 16871 (1995)
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A High-Mobility Germanium QWFET
December 6, 2010 - At IEDM 2009, Intel announced a record breaking quantum well field effect transistor (QWFET); a 35nm
gate length device capable of 0.28mA/μm drive current and peak transconductance of 1350μS/μm. These QWFETs used
InGaAs as the quantum well channel material. At this week’s IEDM 2010 in San Francisco, Intel (Hillsboro, OR) will again
demonstrate a first: a high-mobility germanium QWFET that achieves the highest mobility (770 cm2/Vsec) with ultrathin oxide
Thickness (14.5Å) for low-power CMOS applications. This hole mobility is 4 higher than that achieved in state-of-the-art pchannel strained silicon devices. These results involve the first demonstration of significantly superior mobility to strained
silicon in a p-channel device for low-power CMOS. The biaxially strained germanium QW structure (Figure) 1 incorporates a
phosphorus doped layer to suppress parallel conduction in the SiGe buffers.
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